JP2706324B2 - Light head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for optically reproducing information recorded on a recording medium or optically recording information on a recording medium. CD (Compact Disc) player, LVD (Las
The present invention relates to an optical pickup for reproducing information recorded on an optical disc in a player or the like.

[Conventional technology]

 FIG. 7 shows an example of an optical system of a conventional optical pickup.

The light emitted from the light source 2 is reflected by the beam splitter 5,
The light is focused on the information surface of the recording medium 10 by the objective lens 3.
The light diffracted and reflected by the recorded information returns to the objective lens 3 again, passes through the beam splitter 5, and is received by the photodetector. Thereafter, the detection signal is processed by a circuit (not shown) to obtain a read signal, a focus error signal, a tracking error signal, and the like.

FIG. 8 shows an example of a conventional bulk optical pickup actuator. Although FIG. 7 shows the coil objective lens section 20 and the yoke magnet section 21 vertically separated for the sake of explanation, they are actually integrated.

The coil objective lens unit 20 includes an objective lens 22 for condensing light from a light source and reading recorded information, and a tracking coil 23 for giving a driving force for tracking,
Focusing coil that gives the driving force for focusing
24, and a lead wire 25 that also serves as a suspension and allows current to flow through the coil.

The yoke magnet section 21 includes two magnets 26 and a yoke section 27.

The focusing control and the tracking control at the time of reading are performed by applying a control current to the tracking coil 23 and the focusing coil 24 by a control circuit (not shown) which receives the above-described focus error signal and tracking error signal. Is controlled by changing the position of.

[Problems to be solved by the invention]

The conventional optical pickup actuator has a problem that the number of parts is large, the configuration is complicated, and it is difficult to reduce the size.

In view of the above problems, an object of the present invention is to provide an optical pickup that has a small number of components, has a simple configuration, and is easy to downsize.

[Means for solving the problem]

In order to solve the above problems, the present invention provides an optical head having a light source and an objective lens for condensing light on an optical recording medium, wherein the optical head is divided into a plurality of parts along the optical axis between the light source and the objective lens. The electro-optic effect element having the electrode was placed.

[Action]

According to the present invention, selectively or by applying different voltages to each of the plurality of divided electrodes,
The refractive index in the electro-optic effect element changes. Focusing and tracking can be simultaneously and easily controlled using the change in the refractive index.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS.

First Embodiment A case where the present invention is applied to focusing control of a bulk-type optical pickup will be described with reference to FIG.

First, the control principle will be briefly described. It is known that the refractive index of an electro-optic effect element changes by changing the voltage applied between a pair of electrodes provided on both side surfaces thereof and changing the internal electric field strength. Therefore, by appropriately controlling the voltage, it is possible to arbitrarily control the focus of the reading beam using the change in the refractive index.

In the present embodiment, based on the above principle, the electro-optical effect element 1 is four electrode e ₁ to e ₄ which is divided along the optical axis
And provided between the light source 2 and the objective lens 3.

 Next, the correlation between the applied voltage and the refractive index will be described.

As shown in FIG. 1A, the refractive index of the electro-optic effect element 1 when no voltage is applied to all the electrodes e _{1 to} e ₄ is shown.
and n _0, this time, the light emitted from the light source 2 is transmitted through the electro-optic effect element 1 shall be focused on a point by the objective lens 3.

When a voltage is applied between the electrode e ₃ and the electrode e ₄ as shown in FIG. 1B, the refractive index n ₁ of the electro-optic effect element between the electrode e ₃ and the electrode e ₄ is larger than the initial refractive index n _0. Become. Therefore, the condensing point moves to point b closer to the objective lens than point a. As shown in FIG. 1 (c), further electrodes e ₁ - If also a voltage is applied between the electrodes e _2, the electrode e ₁ - refractive index n ₂ of the electro-optic effect device between the electrodes e ₂ initial refractive index n _0, which is closer to the objective lens as compared with FIG. 1 (b).
The focal point moves to the point. As described above,
By applying an arbitrary voltage between the electrodes, light from the light source can be collected at an arbitrary position.

Next, a case where the present invention is applied to tracking control of a bulk-type optical pickup will be described with reference to FIG.

First, the control principle will be briefly described. It is assumed that a substance having parallel end faces is placed on a plane such that each end face is perpendicular to the plane. When light parallel to the plane is obliquely incident on one end face of the substance, the outgoing light is emitted from the other end face in a direction parallel to the incident light, and the emission position shifts parallel to the plane according to the refractive index. Therefore, the tracking of the read beam can be arbitrarily controlled by appropriately controlling the voltage applied to the electrode of the electro-optic effect element to control the refractive index.

Based on the above principle, among the electrodes provided in the electro-optical effect element in the present embodiment, they are not opposed to each other,
In addition, tracking is controlled by applying a voltage between non-adjacent electrodes.

As shown in FIG. 2B, the refractive index of the electro-optical effect element 1 when no voltage is applied to all the electrodes e _{1 to} e ₄ is shown.
and n _0, light emitted from the light source 2 shall be focused on a point by the objective lens 3 is transmitted through the electro-optic effect element 1. When a voltage is applied between the electrode e ₂ and the electrode e ₃ as shown in FIG. 2A, the refractive index n ₁ of the electro-optic effect element 1 between the electrode e ₂ and the electrode e ₃ becomes larger than the initial refractive index n ₀ . growing. Therefore, the focal point will be compared to a point, it is focused on the right side of a _1-point drawing on the optical axis. When a voltage is applied between the electrode e ₁ and the electrode e ₄ as shown in FIG.
Compared to a point, it will be focused on the left side of a _2-point drawing on the optical axis. Not facing each other as described above, and
Tracking control can be easily performed by applying a voltage between electrodes that are not adjacent to each other.

The case where focusing and tracking are performed simultaneously will be described with reference to FIG.

Here, regarding focusing, electrode e ₁ −electrode e ₂
No voltage is applied between the electrodes e ₃ and e ₄ , and a voltage of 1 · E (where E is an arbitrary voltage) is applied between the electrodes e ₃ and e ₄ (FIG. 3A), and all electrodes e _The case where a voltage of 0.5 · E is applied to _{1 to} e ₄ (FIG. 3B) is equivalent, and all the electrodes e _{1 to} e ₄
When a voltage of 1 · E is applied to the electrode (FIG. 3 (c)), no voltage is applied between the electrodes e ₁ and e _2, and a voltage of 2 · E is applied between the electrodes e ₃ and e _4. (FIG. 3D) is regarded as equivalent. On the other hand, regarding tracking, the electrode e ₂ −electrode
When a voltage of 1 · E is applied between e ₃ and the focal position is shifted by x from the optical axis (FIG. 3 (e)), the electrode e ₂ −
When a voltage is applied of 2 · E in between the electrodes e ₃ in (FIG. 3 (f)) and shall focus position is shifted by twice the 2x.

According to the above, as shown in FIG. 3 (g), the electrode e ₁ −
Between the electrodes e ₄ by applying a voltage of 0.5 · E, the electrode e ₂ - when applying a voltage of 1.5 · E between the electrodes e ₃ are the same focal length as that of FIG. 3 (c), The focus position can be shifted from the optical axis by x.

Second Embodiment FIG. 4 shows a second embodiment in which the present invention is applied to an integrated optical pickup.

In the integrated optical pickup P, a semiconductor laser 2a is provided on one end side of the optical integrated circuit board B, and light injected from the semiconductor laser 2a is collected by a focusing grating through a waveguide formed in the optical integrated circuit board B. The coupler 4 is guided so that the beam spot S is focused on the information recording surface by the objective lens function of the focusing grating coupler 4.
Then, the reflected beam reflected by the information recording surface returns to the condenser grating coupler 4 again, is guided to the Foucault prism 7 by the beam splitter 5 via the waveguide, and is incident on the photodetector 6. The photodetector 6 generates an output voltage corresponding to the incident light beam, and obtains a focus error signal, a tracking error signal, and a read signal by calculating a difference between the output signals by a calculator (not shown). Known examples of such an optical integrated type optical pickup include the examples described in "Optical integrated disk pickup head" (Optronics (1989), Japanese Patent Application Laid-Open No. 61-296540).

As shown in the above optical integrated type optical pickup,
The electro-optic effect element 1 having _four electrodes e _{1 to} e 4 along the optical axis is provided between the beam splitter 5 and the condenser grating coupler 4. Light emitted from the semiconductor laser 2a passes through the beam splitter 5 and is guided into the electro-optic effect element 1. Here, focusing control and tracking control are performed by changing the refractive index of the electro-optical effect element 1 and changing the light condensing position based on the above-described focusing error signal and tracking error signal.

Third Embodiment As shown in FIG. 5, an optical modulator 8 for performing optical modulation
And a recording signal generator 9 for controlling the optical modulator 8 based on information to be recorded, between a light source (for example, a semiconductor laser) and an objective lens (or a focusing grating coupler). For example, it can be used as a recording optical head. Further, by providing a beam splitter, a Foucault prism, a photodetector, and the like, it is possible to configure an optical head capable of reading and recording recorded information.

Fourth Embodiment In the above, only the case where the opposing electrodes are provided in parallel with the optical axis interposed therebetween has been described. However, as shown in FIG. 6, each electrode can be arranged at an angle. . Further, in each of the embodiments described above, only the case where the number of electrodes is four has been described. However, more detailed control can be performed by increasing the number of electrodes.

〔The invention's effect〕

Since the present invention is configured as described above, it is possible to easily perform the focus control and the tracking control without providing a movable part, and to provide an effect that the optical head can be downsized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of the focusing control in the present invention, FIG. 2 is an explanatory diagram of the tracking control in the present invention, FIG. 3 is an explanatory diagram in a case where the focusing and tracking control are performed simultaneously, and FIG. FIG. 5 is a schematic diagram of a third embodiment of the present invention, FIG. 6 is a schematic diagram of a fourth embodiment of the present invention, FIG. 7 is an explanatory diagram of a conventional optical system, FIG. FIG. 8 is an explanatory view of a conventional optical pickup. DESCRIPTION OF SYMBOLS 1 ... Electro-optic effect element 2 ... Light source 3 ... Objective lens 4 ... Condensing grating coupler 5 ... Beam splitter 6 ... Photodetector 7 ... Foucault prism 8 ... Optical modulator 9 ... Recording signal Generator B Optical integrated circuit board e _{1 to} e ₄ Electrode P Optical pickup

Claims (1)

(57) [Claims] 1. An optical head comprising a light source and an objective lens for converging light on an optical recording medium, comprising: an electro-optical device having a plurality of divided electrodes along the optical axis between the light source and the objective lens. An optical head comprising an effect element.